Antimicrobial and Cytotoxic Lysolipins I-M Isolated from Streptomyces sp. P8-2B18
Lysolipin I (1) is a highly bioactive xanthone with strong antibacterial and cytotoxic properties. Given the limited number of lysolipin analogues, discovery of new natural lysolipin derivatives is important for understanding their structure-activity relationships. A soil-derived Streptomyces sp. P8-2B18 harbors a putative lysolipin biosynthetic gene cluster and LC-MS based metabolomic analysis revealed the production of lysolipin I along with unreported analogues. Large-scale fermentation followed by isolation led to the discovery of four new analogues, lysolipins J-M (2- 5), the structures of which were elucidated by mass spectrometric and NMR spectroscopic data analyses. Lysolipin L features a five-membered lactam F ring, which was unprecedented in reported lysolipins. Lysolipin M has a novel skeleton, with an extra methyl (Me-36) and a glycosyl group replacing a 1,3-oxane ring in lysolipin I. While lysolipins I, J and K displayed strong activity against Staphylococcus aureus and Aspergillus flavus with MIC values ranging from 0.25 to 4 g/mL and lysolipin L showed only moderate activities, lysolipin M was inactive (>50 g/mL). Lysolipins I-K showed potent cytotoxic activity against prostate cancer cell lines LNCaP and C4-2B, with IC50 values in the submicromolar range. In contrast, lysolipin L exhibited no cytotoxicity and lysolipin M exhibited substantially reduced potency. Their broad, non-selective bioactivities restricted their applicability as therapeutic agents.